1. Technical Field
This disclosure relates to optical sensors, including rotational optical sensors configured to measure the rotation of a steering wheel in a vehicle and the torque that is applied to it.
2. Description of Related Art
Sensors may be used to determine rotational position, such as the position of a shaft attached to a steering wheel in a vehicle. The sensors may also determine the torque that is applied to the steering wheel by measuring the angular displacement between two different shafts which are attached to one another through a torsion rod.
Some sensors couple a potentiometer to each rotating shaft to make these angular measurements. However, potentiometers may fail to operate due to surface contamination and/or wear related to sliding contacts.
Magnetic sensors may couple a magnet to each rotating shaft and may use a magnetic field detector to make these angular measurements. However, stray magnetic fields and variations in magnet strength may reduce the precision of the sensors. The components may also be costly.
Optical sensors may couple a disk to each rotating shaft to make to these angular measurements. Each disk may have an annular pattern which alternates between different levels of optical transparency. A light source and associated optical sensing array may be used to detect a portion of the combined pattern from both disks, which may then be translated into the angular positions. However, it may be costly to manufacture and assemble the components, such as the patterns on the disks, to within a sufficient degree of tolerance so as to achieve needed accuracy, such as to achieve an accuracy of ±0.02 degrees. Such sensors may also have to be aligned to a key in the shaft in order to function properly. This may add to the cost of the shaft and to the installation procedure.